Frankly, a good wash a couple times a week (punctuated by a bird bath in the sink and perhaps a sprinkling of dry shampoo) would do the trick. How do I know? Because I'm a card-carrying member of the infrequent showerers club. Plus, the less you lather up with all that alluring tat from the supermarket shelf, the less you'll be using loads of things that aren't exactly great for you (especially in larger quantities), like triclosan and the aluminium additives in so many anti-perspirant brands (no, there's no direct link to breast cancer on this last one but ask someone who has had it what the first thing was the doctor told them to do... it will usually be to immediately stop using their deodorant/anti-perspirant. True story.)